Microelectronic-Mechanical Systems (MEMS) devices include a variety of micron or nano-scale devices such as switches, sensors (e.g., chemical sensors), gyroscopes, accelerometers, and atomic clock devices. Due to the small scale of these devices and their components, the devices require manufacturing processes that allow for the production of small scale features, without contaminating or altering the desired chemical makeup of the components of the device.
MEMS devices are important for their highly precise and accurate measurement capabilities. A specific example of a MEMS device, an atomic clock, can be used in various systems that require extremely accurate and stable frequencies, such as in bistatic radars, global positioning systems, and other navigation and positioning systems, as well as in communications, cellular phone systems, and scientific experiments, for example.
One type of atomic clock known as a cell type atomic clock operates by simultaneously irradiating an active medium with optical power and microwave power. The optical power pumps the active atoms, usually rubidium or cesium, to make the medium absorbing at the microwave frequency corresponding to transitions between the two hyperfine levels of the ground state. It is desirable to have the longest amount of time possible to measure the energy levels (frequency) of such atoms. One way to obtain a long measurement time is to keep the atoms in one place while measuring them. One way of doing this is to contain the atoms in a cavity or cell, for example. Generally, such cell structures provide a vacuum environment wherein the active medium can be controllably provided as a vapor.
An RF switch is an active RF component that switches a single input between one or more outputs. RF switches also can include a cavity that contains an extremely small amount of a functional material, e.g., liquid galliums.
Because certain materials that are used in MEMS devices, e.g., rubidium, cesium, gallium, alkali metals, etc., can be extremely reactive, processing these materials can be difficult. In general, these materials need to be carefully handled such that they are not exposed to atmosphere thereby initiating undesirable reactions or introducing contamination.